1. Field of the Invention
The present invention relates to an oxide magnetic material to be used in various electronic parts, and a chip part formed with the oxide magnetic material and including a bulk-type coil part and an internal conductor for inductance to be used in a high frequency area, as well as a method of producing the oxide magnetic material, and to a method of producing the chip part.
2. Description of the Related Art
Nixe2x80x94Cuxe2x80x94Zn based ferrite is generally used as an oxide magnetic material such as coil parts and the like to be used in a high frequency area. A powder metallurgical method is general for producing the same. According to this method, oxides such as Fe2O3, NiO, CuO, ZnO and the like to be starting materials are weighed so as to be predetermined ratios, and are then dry- or wet-mixed and crushed, and this mixed powder is temporarily baked. Subsequently the temporarily baked matter is roughly crushed and is further pulverized. In case the oxide is wet-crushed, the powder is required to be dried. Here, properties of ferrite considerably depend on the composition; therefore, the divergence of composition should be kept extremely small from the viewpoint of production control. Further, material for laminated coil is required to be baked at a lower temperature than the melting point of Ag, and the composition control is required to be at a level of 0.1 mol % of Fe2O3, NiO, CuO or ZnO. Especially as to Fe2O3, reactivity increases as coming near to the stoichiometrical composition of ferrite, but when exceeding it, the reactivity abruptly decreases; therefore, among the main constituents of ferrite, a most serious composition control is needed.
For conventional Nixe2x80x94Cuxe2x80x94Zn ferrite, stainless steel balls, alumina balls, zirconia balls and other have been used as medium beads in the production process, and crushed with mixing, temporarily baked, roughly crushed and further pulverized. The bulk-type coil material is normally temporarily baked and crashed such that a specific surface area is around 1.0 to 6.0 m2/g. The laminated coil material is, however, crushed for a long time because it is required to be baked at a lower temperature than the melting point of Ag, thereby to increase the specific surface area up to around 3.0 to 15.0 m2/g to heighten the reactivity of powder at low temperature.
Here, the stainless steel balls have Fe as a main constituent, and due to mechanochemical reaction during crushing, Fe2O3 which is a main constituent of Nixe2x80x94Cuxe2x80x94Zn ferrite is increased. The increase of Fe2O3 changes the composition of Nixe2x80x94Cuxe2x80x94Zn ferrite and causes a stabilized composition control to be difficult. That is, it is difficult to control the composition with weighed quality values. Other medium beads have a defect in abrasion resistibility, and a defect that abraded powders of the medium beads are mixed into the crushed powder as impurities.
Further, the general medium beads have the inner side of abrasion resistibility which is lower than that of the outer side. Therefore, it causes a divergence in the composition due to the difference in mixing amount of powder produced by abrasion as the production goes on, and it is impossible to obtain stable composition. The crushing for a long time will invite the increase of the amount of the abraded powder, deteriorating the property of baked material. Namely, the abraded powder mixed as impurities will deteriorate the sintering property of Nixe2x80x94Cuxe2x80x94Zn ferrite, thereby to cause the baking temperature to be high for obtaining the density and permeability of sintered material with the neighborhood of a theoretical density. This will invite a high production cost and decrease of stability in products, and further will make it difficult to bake the sintered material at lower temperature than the melting point of Ag.
The Japanese patent No. 2708160 discloses, for the purpose of reducing the mix of abraded powder at the time of crushing, the use of balls of fully stabilized zirconia (FSZ) of high abrasion resistibility or of partially stabilized zirconia (PSZ) as medium beads for crushing Mnxe2x80x94Zn based ferrite. According to the method of this patent document, the zirconia balls of a diameter 0.5 to 3.0 mm are used as medium beads in the pulverizing process to extremely prevent impurities from being mixed, thereby to suppress the mixing amount to be less than 0.02 wt % relative to the main constituent. It is described in this patent document that with this method, the powder may be sintered at temperature lower by about 100 to 200xc2x0 C. (that is, at approximately 1000xc2x0 C.) in contrast to the temporarily baking temperature of 1200xc2x0 C. or higher of the conventional art to obtain the sintered material with the neighborhood of theoretical density, thus to industrially lower the sintering temperature and reduce the production cost. Further, JP-A-7-133150 discloses a sample having ZrO of 0.01 to 3.0 wt % relative to the main constituent of Nixe2x80x94Cuxe2x80x94Zn ferrite and baked at the temperature of 1100xc2x0 C. for 1.5 hours for the purpose of providing a magnetic material of high mechanical strength.
However, the baking temperature of approximately 1000xc2x0 C. described in the Japanese patent No. 2708160 will not actually reduce the baking cost and will not be adapted to the simultaneous baking with Ag of melting point of approximately 960xc2x0 C. The baking temperature of approximately 1100xc2x0 C. as described in JP-A-7-133150 will be further impossible for the simultaneous baking with Ag.
Further, according to the production method of the Japanese patent 2708160, medium beads of small diameter are used to reduce the amount of impurities mixed into the material due to the abrasion of the medium beads, and the temporarily baked material is crushed, taking a long time, for example, 196 hours. Therefore, the ball efficiency ([material processing amount]/[ball weight]), that is, the crashing efficiency is bad.
In consideration of the above mentioned problems, it is an object of the invention to provide an oxide magnetic material which can be subjected to a low temperature baking with holding sintering property and permeability and shortening the crushing time, and to provide a chip part formed by use of the same. In addition, it is also an object of the invention to provide a method of producing the oxide magnetic material and a method of producing the chip part.
According to a first aspect of the invention, the oxide magnetic material is characterized by containing Fe2O3, ZnO, CuO and NiO as main constituents, and further containing Y2O3 of 0.003 to 0.021 wt % and ZrO2 of 0.06 to 0.37 wt % in the main constituents with respect to all amounts.
As additives to the main constituents, it is also preferable that the oxide magnetic material further contains Si of 0.010 to 0.112 wt % (including the cases where Si is contained as silicon oxide) in the main constituents with respect to all amounts.
Further, as additives to the main constituents, it is also preferable that the oxide magnetic material further contains Y2O3 of 0.001 to 0.011 wt %, ZrO2 of 0.03 to 0.194 wt %, and Si of 0.010 to 0.056 wt % (including the cases where Si is contained as silicon oxide) in the main constituents with respect to all amounts.
So far as giving no influence to the properties such as the permeability or the density of the baked material, Si, P, Al, B, Mn, Mg, Co, Ba, Sr, Bi, Pb, W, V, Mo and the like may be included as impurities. For obtaining a permeability higher than a predetermined value, the composition of main constituents is preferably Fe2O3 of 40 to 51 mol %, ZnO of 1 to 34 mol %, CuO of 1 to 30 mol % and the balance being NiO. More preferably, Fe2O3 is 46 to 50 mol %, ZnO is 32 to 34 mol %, CuO is 9 to 11 mol % and NiO is 8 to 11 mol %.
In case the partially stabilized zirconia ball (PSZ) containing Y2O3 is used to crush the temporarily baked powder, it is known that the partly stabilized zirconia ball having Y2O3 containing about 3 mol % is most excellent in hardness and destructive toughness value (Strong Zirconia-Tough Ceramics, written by HORI, Saburou, issued from Uchida Roukakuen). For trying to obtain the crushed powder of average particle diameter of approximately 0.1 to 1.0 xcexcm, if the composition is Y2O3 of less than 0.003 wt % and ZrO2 of less than 0.06 wt %, it is required to crush the powder, delaying an agitating rate and taking a long time. However, if the composition is more than these weight percents, the crushing efficiency may be heightened and the crushing is possible at a shorter time, though depending on the size of ball diameter and agitating rate. On the other hand, if Y2O3 exceeds 0.021 wt % and ZrO2 exceeds 0.37 wt %, it is difficult to obtain an apparent density of 5.0 g/cm3 or more which is said to be not problematical about the physical strength at 920xc2x0 C. where a simultaneous baking with Ag is possible. Therefore, the baking temperature should be raised in order to secure the apparent density. Further, if Y2O3 exceeds 0.021 wt % and ZrO2 exceeds 0.37 wt %, the permeability may be deteriorated.
In the case where the oxide magnetic material further contains Si as additives to the main constituents, for trying to obtain the crushed powder of average particle diameter of approximately 0.1 to 1.0 xcexcm, if the composition is Si of less than 0.010 wt %, it is required to crush the powder, delaying an agitating rate and taking a long time. However, if the composition is more than these weight percents, the crushing efficiency may be heightened and the crushing is possible at a shorter time, though depending on the size of ball diameter and agitating rate. On the other hand, if Si exceeds 0.112 wt %, it is difficult to obtain an apparent density of 5.0 g/cm3 or more which is said to be not problematical about the physical strength at 920xc2x0 C. where a simultaneous baking with Ag is possible. Therefore, the baking temperature should be raised in order to secure the apparent density. Further, if Si exceeds 0.112 wt %, the permeability may be deteriorated.
In the case where the oxide magnetic material further contains Y2O3, ZrO2, and Si as additives to the main constituents, for trying to obtain the crushed powder of average particle diameter of approximately 0.1 to 1.0 xcexcm, if the composition is Y2O3 of less than 0.001 wt % and ZrO2 of less than 0.031 wt %, and Si of less than 0.010 wt %, it is required to crush the powder, delaying an agitating rate and taking a long time. However, if the composition is more than these weight percents, the crushing efficiency may be heightened and the crushing is possible at a shorter time, though depending on the size of ball diameter and agitating rate. On the other hand, if Y2O3 exceeds 0.011 wt % and ZrO2 exceeds 0.37 wt % and Si exceeds 0.056 wt %, respectively, it is difficult to obtain an apparent density of 5.0 g/cm3 or more which is said to be not problematical about the physical strength at 920xc2x0 C. where a simultaneous baking with Ag is possible. Therefore, the baking temperature should be raised in order to secure the apparent density. Further, if Y2O3 exceeds 0.011 wt % and ZrO2 exceeds 0.194 wt % and Si exceeds 0.056 wt %, the permeability may be deteriorated.
A chip part according to a second aspect of the invention is characterized by using a sintered material of the oxide magnetic material which is described in the first aspect of the invention so as to be formed as a bulk-type coil part.
As the chip part according to the second aspect is composed by using the oxide magnetic material which is defined in the first aspect of the invention, the chip part is baked at a low temperature and is provided at a low cost while sufficiently coping with the one baked at a high baking temperature with respect to the strength and permeability.
A chip part according to a third aspect of the invention is characterized by using the sintered material of the oxide magnetic material according to the first aspect, and having an electric conductor layer in the sintered material, the chip part having a laminated coil part or partly having the laminated coil part.
The chip part according to a fourth aspect of the invention is characterized in that an internal conductor has Ag or an alloy of Ag and Pd as a main constituent in the tip part according to the third aspect.
As the chip part according to the third and fourth aspect of the invention is formed by use of the oxide magnetic material according to the first aspect, the chip part has substantially the same strength and permeability as the chip part according to the second aspect, and further can be baked simultaneously with Ag and the alloy of Agxe2x80x94Pd.
A fifth aspect of the invention is that a method for producing the oxide magnetic material according to the first aspect, characterized in that medium beads of partially stabilized zirconia are used at a time of mixing and crushing raw material and at a time of crushing a temporarily baked material, and Y2O3 of 0.003 to 0.021 wt % and ZrO2 of 0.06 to 0.37 wt % is contained therein with respect to all amounts in the oxide magnetic material by wear of the medium beads.
Thus, if the partially stabilized zirconia balls is used to crush the material after being temporarily baked, it is possible to eliminate the difficult problem in the composition control as using the conventional stainless steel balls or the like. Further, since Y2O3 and ZrO2 are mixed into the material through the crushing process, the process for weighing and mixing the constituent into the material may be eliminated.
In the fifth aspect of the invention, it is also preferable that silicon nitride is used as medium beads and that Si of 0.010 to 0.112 wt % is contained with respect to all amounts in the oxide magnetic material by wear of the medium beads.
Thus, if the silicon nitride balls are used to crush the material after being temporarily baked, it is possible to eliminate the difficult problem in the composition control as using the conventional stainless steel balls or the like. Further, since Si is mixed into the material through the crushing process, the process for weighing and mixing the constituent into the material may be eliminated.
Further, in the fifth aspect of the invention, it is also preferable that partially stabilized zirconia and silicon nitride are used as medium beads at a time of mixing and crushing raw material and at a time of crushing a temporarily baked material by means of the media agitating mill of the wet internal circulation type. By wear of the medium beads, Y2O3 of 0.001 to 0.011 wt %, ZrO2 of 0.03 to 0.194 wt %, and Si of 0.010 to 0.056 wt % are contained with respect to all amounts in the oxide magnetic material.
Thus, if balls of partially stabilized zirconia and silicon nitride are used to crush the material after being temporarily baked, it is possible to eliminate the difficult problem in the composition control as using the conventional stainless steel balls or the like. Further, since Y2O3, ZrO2, and Si are mixed into the material through the crushing process, the process for weighing and mixing the constituent into the material may be eliminated.
Moreover, in the fifth aspect of the present invention, it is preferable that the volume ratio of the silicon nitride beads is in the range between 20% and 99% with respect to the total amount of partially stabilized zirconia beads and silicon nitride beads.
Due to the above ratio of partially stabilized zirconia beads and silicon nitride beads, mixing of ZrO2 and Y2O3, which are main constituents of partially stabilized zirconia beads, is further facilitated by means of wear of the medium beads, compared with the case where only partially stabilized zirconia beads are used to crush the material.
According to a sixth aspect of the invention, a method for producing the oxide magnetic material in the fifth aspect is characterized by using material as medium beads having diameter of 0.2 to 5 mm.
In the case where the medium beads are of a diameter less than 0.2 mm, the crushing efficiency is lowered. On the other hand, in the case where the diameter exceeds 5 mm, the powder will not be sufficiently pulverized, and the sintering temperature will become high for obtaining a density of sintered material with the neighborhood of theoretical density and the permeability will be deteriorated.
According to a seventh aspect of the invention, a method for producing the oxide magnetic material in the fifth or sixth aspect is characterized in that agitating rate of the medium beads is 2.0 to 8.0 m/s.
In the case where the agitating rate of the medium beads is lower than 2.0 m/s, it will take a long time to crush the material until a desired specific surface area is obtained. This is not reasonable in consideration of the lead time pertaining to the production of material. On the other hand, if exceeding 8.0 m/s, the abrasion of beads is increased, and the baking temperature becomes high for obtaining the density of a sintered material with the neighborhood of the theoretical density and a desired permeability, inviting the increase of production cost, the lowering of stabilization of products, and further making it difficult to bake the material at a temperature lower than the melting point of Ag.
According to an eighth aspect of the invention, the method in one of fifth to seventh aspects is characterized by obtaining powders of specific surface area of 6.0 to 15.0 m2/g by crushing from the material after having been temporarily baked.
In the case where the specific surface area is less than 6.0 m2/g, the baking temperature becomes high for obtaining the density of the sintered material in the neighborhood of the theoretical density, inviting the deterioration of the permeability. In the case where it is more than 15.0 m2/g, the crushing time will be long.
According to a ninth aspect of the invention, the method in the third or fourth aspect is characterized by forming an oxide magnetic material crushed by medium beads and an internal conductor and by baking at a certain temperature range. If partially stabilized zirconia is used as medium beads, the temperature range is between 880 and 920xc2x0 C. If silicon nitride is used as medium beads, the temperature range is between 910 and 920xc2x0 C. If partially stabilized zirconia and silicon nitride are used as medium beads, the temperature range is between 910 and 920xc2x0 C.
In the case where the baking temperature is lower than the above range, the sintering is insufficient. In the case where exceeding the above range, the electrode material is diffused in ferrite to extremely deteriorate the magnetic property of chip. In this method, the baking time is about 5 minutes to 3 hours.
The oxide magnetic material for a bulk-type coil part or a laminated coil part or other electronic parts according to the invention is a ferrite material containing the main constituents of Fe2O3, ZnO, NiO, and CuO, and containing, if needed, the slight amounts of weighed additives such as Si, P, Al, B, Mn, Mg, Co, Ba, Sr, Bi, Pb, W, V, Mo and the like, and further containing, as sub-constituents, ZrO2 and Y2O3 which are mixed into the material due to abrasion of partially stabilized zirconia balls as the medium beads. It is also preferable that the ferrite material further contains, as sub-constituents, Si which is mixed into the material due to abrasion of silicon nitride balls as the medium beads. Furthermore, it is also preferable that the ferrite material further contains, as sub-constituents, ZrO2, Y2O3, and Si which are mixed into the material due to abrasion of partially stabilized zirconia balls and silicon nitride balls as the medium beads. With adjustment of the particle size of the medium beads, agitating rate, agitating time at time of crushing raw materials and at time of crushing the material after being temporarily baked, the mixing amount of the medium beads is adjusted, and the baking temperature is not required to be heightened. Therefore, the baking may be available at temperature lower than the melting point of Ag.
The materials weighed as mentioned above are mixed and crushed by means of the media agitating mill of the wet internal circulation type with at least one of the partially stabilized zirconia balls and silicon nitride balls as the medium beads. Subsequently, the crushed material is temporarily baked and crushed by means of the media agitating mill of the wet internal circulation type with the partially stabilized zirconia balls as the medium beads, thereby to obtain the oxide magnetic material.
A core for the bulk-type coil is made up by adding a binder to the oxide magnetic material produced as mentioned above and is granulated, followed by molding into a predetermined shape, processed and baked at 900 to 1300xc2x0 C. in the air. The core may be processed after baking. The core is made by winding a wire therearound, the wire being of Au, Ag, Cu, Fe, Pt, Sn, Ni, Pb, Al, Co or an alloy thereof.
On the other hand, the laminated coil is normally produced by laminating into one body a paste of the magnetic layer of the oxide magnetic material and an internal conductor layer by means of a thick filming technique (printing process or the doctor blade method), then baking, subsequently printing the thus obtained sintered material on the surface thereof with a paste of an external electrode and baking. The internal conductor paste contains normally an electrically conductive element, a binder and a solvent. The material for the electrically conductive element is preferred to be an alloy of Agxe2x80x94Pd for a reason of increasing the quality coefficiency Q of inductor. The baking condition and baking atmosphere may be appropriately determined in consideration of the property and other of the magnetic material and electrically conductive element, and the baking temperature is preferred to be approximately 800 to 950xc2x0 C. More preferably, the baking temperature is about 880 to 920xc2x0 C. in the case where the partially stabilized zirconia balls are used as medium beads and about 910 to 920xc2x0 C. in the case where silicon nitride balls or both the partially stabilized zirconia balls and silicon nitride balls are used.